[Augustin teaches the Nicene doctrine of a numerical unity of essence in distinction from a specific unity. The latter is that of mankind. In this case there is division of substance—part after part of the specific nature being separated and formed, by propagation, into individuals. No human individual contains the whole specific nature. But in the case of the numerical unity of the Trinity, there is no division of essence. The whole divine nature is in each divine person. The three divine persons do not constitute a species—that is, three divine individuals made by the division and distribution of one common divine nature—but are three modes or “forms” (Phil. ii. 6) of one undivided substance, numerically and identically the same in each.—W.G.T.S.]